Modelagem de bobinas bifilares no formato espiral plano quadrado simétrico em aberto

Abstract

Since the 1990s, researches on modeling of planar spiral coils (PSC) were primarily driven by a market trend that gradually required the manufacture of as more and more compact passive devices for wireless technologies design. However, in general, these studies are limited to modeling of monofilar PSCs and planar transformers manufactured on silicon substrate, with up to a dozen turns and operating at the GHz range. Currently, the modeling of bifilar PSCs with dozens of turns, manufactured on FR-4 substrate and operating at MHz is still little researched. The bifilar PSC operation at lower frequencies (MHz) is an advantage, for example, in biomedical applications where the remotely received signal of a sensor implanted in a biological tissue tends to be less attenuated with decreasing frequency. Therefore, a research was developed on modeling of bifilar PSCs in order to study their electrical behavior up to around the first resonance peak. An electrical model of square bifilar PSC on symmetrical shape in open-circuit configuration was developed, their electrical parameters (resistances, conductances, inductances, and capacitances), expressions for the first self-resonance frequencies (valley and peak) as well as the input impedance of the bifilar PSC were determined. Also noteworthy are the new approaches presented for the determination of the stray capacitances that arise between the metal tracks of bifilar PSC and the conductances associated with its dielectric materials. A set of square bifilar PSCs of FR-4 substrate was manufactured, which electrical parameters and input impedances were measured by an impedance analyzer, as well as the layout of each bifilar PSC was submitted to electromagnetic simulations. Finally, the results of the research were presented in tables and graphs, with the aim of comparing the theoretical results of the proposed model with those obtained by electromagnetic simulations and measured values. It was concluded that the electric model and developed expressions prove feasible and promising for the modeling of square bifilar PSCs in open-circuit configuration, when the analysis is restricted to the study of the electrical behavior up to surrounding the first resonance peak.